Integrated circuits (ICs) form the basis for many electronic systems. Essentially, an integrated circuit (IC) includes a vast number of transistors and other circuit elements that are formed on a single semiconductor wafer or semiconductor chip and are interconnected to implement a desired function. Increasing complexity of these ICs leads to an increasing number of linked transistors and other circuit elements.
Many modern electronic systems are created through the use of a variety of different ICs each performing one or more specific functions. For example, many computer systems include at least one microprocessor chip and a number of memory chips. The microprocessor chip and memory chips can be formed on separate chips, packaged independently, and interconnected on, for example, a printed circuit board (PCB).
As IC technology has progressed, there have been attempts to combine the functionality of IC devices which are fabricated on separate wafers or chips to provide benefits such as reduced packaging size and/or increased system performance. Examples of such combinations include a chip on chip (COC) approach in which one chip is stacked on another chip, a multi-chip module (MCM) approach in which multiple chips are stacked on a common substrate, and a “system on a chip” approach in which a single chip includes all of the IC devices of a system.